Miniaturization of VHF Band Lumped-Element Filters on Multilayer Printed Circuit Boards

This letter presents a miniaturized scheme for very high-frequency (VHF) lumped-element filters based on the surface mount technology (SMT) and the multilayer printed circuit boards (PCBs) using chip capacitors and multilayer stacked spiral inductors. Meanwhile, the parasitic coupling among the spiral inductors is reduced by layout optimization and metallic layer isolation. In addition, to compensate for the fabrication errors in the multilayer PCBs, the parallel capacitor pairs are introduced, and the prepreg layers thickness is modified in the simulation. To validate the scheme, a seventh-order quasi-elliptic function filter with superior out-of-band rejection is designed with compact structures, including up to 39 lumped elements. By replacing the capacitor pairs, the significant frequency shift and narrowing of the passband between the initially measured results and the simulated ones can be eliminated, and the tuned results are in excellent consistency with the simulation.